Wool.
The fleece of sheep and other animals. That of sheep was used for weaving into cloth, and is generally referred to as 'wool.' In the figurative language of Isaiah 1:18 undyed wool represents the state resulting from the removal of sin by Jehovah from His people; the sin being compared to that which had been dyed crimson. The law forbade the wearing of a garment made of linen and wool: it was an unnatural mixture, figurative of the working of the Spirit and the flesh in a Christian. Leviticus 19:19; Deuteronomy 22:11.